Weeds are a tremendous problem of farmers and growers throughout the world. For example, it has been reported that cogongrass (Imperata cylindrica) is one of the ten worst weeds worldwide and has become firmly established in the Southeastern United States, especially in areas where tillage is not the principle method of weed control. Cogongrass grows best in relatively acidic soils that are low in fertility and highly leached.
To date the only fungi reported on hosts in the genus Imperata in the United States are two species of rust found on Imperata brevifolia Vasey in Arizona. Farr et al., Fungi on Plants and Plant Products in the United States, APS Press, St. Paul, Minn. (1989). There is no listing of the genus Imperata as a host of fungus in the state of Florida. Alfieri S A Jr. et al., Diseases and Disorders of Plants in Florida, Division of Plant Industry Bulletin 14, Gainesville (1994). In international lists of agriculturally important fungi, Imperata cylindrica is either not listed or is listed with only rust species. Viegas, Indite de Fangos da America do Sol, Instituto Agronomico, Campinas, Brazil (1961).
Current methods of controlling cogongrass include chemicals and mechanical practices, such as disking, mowing, and burning. However, the most widely used weed control practice is the use of chemical herbicides which poses ecological concerns of introducing toxic and sometimes non-biodegradable substances into the ecosystem. Other issues with use of chemical herbicides include lack of residual control, injury to non-target organisms, undesirable residues in harvested products, and carryover in subsequent crops.
A more recently used practice for managing cogongrass is the use of native grass species to compete with cogongrass. While use of native grass as a biocontrol is important both environmentally and biologically, it has been observed that the use of native grass species as a biocontrol in the short term is slow and less effective when compared to chemicals and less certain when compared to chemical and mechanical control practices.
In light of the concerns with chemical herbicides, there is a demand for biological control methods. In the field of herbicides, extensive investigations have been carried out on biologically based herbicides, such as mycoherbicides, which use a fungus that is pathogenic to the weed. For example, U.S. Pat. No. 4,606,751 to Van Dyke et al., teaches using the fungus Bipolaris sorghicola as a mycoherbicide to control Johnson grass (Sorghum halepense). However, there are no bioherbicides yet available against cogongrass.
With the foregoing in mind, it is an object of the present invention to provide bioherbicide methods and compositions for controlling cogongrass and similar wild grassy weeds.